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This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical dq-transformation techniques. This paper presents a new dq synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of q axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated: (1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter DC link via the antiparallel diodes; and (2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.